Gordon is correct. When uni-directional printers are used, the film is normally printed heads-to-tails. So after processing the large rolls, the film is oriented tails-to-heads. The trailers are then spooled off the large roll heads-to-tails, which is the way you normally receive them.

Some labs use "loop" type printers for the majority of their bulk release work, printing release prints heads-to-tails. But bi-directional printers like those made by BHP are still widely used too:http://www.rti-us.com/bhp/